streamed video appears delayed by hours!

[anagram]

I've been running Zoneminder 1.25.0 (and previous versions) for several years, and last year installed a Camsecure 8-channel pcie card (5008) which uses the Philips SAA7130HL chipset.

It has been working fine, but increasingly I'm getting a very weird error: about once a week the system goes into a state that superficially looks fine, but no alarm triggers are generated and on closer inspection the images streaming from the server are from hours in the past! It's not a frozen image -- you can see normal motion -- but it's at a reduced frame rate. The timestamps are for the current time though, indicating the the images are getting buffered somewhere before the timestamps are added.

I am using 6 of the 8 channels at 288x384, with a frame rate of 5 fps, and very litle cpu load. Looking at the logs, what seems to happen is the frame rate drops to 4.98 then to 2.19 and then to 2 fps over about 20 minutes and then sticks on 2 fps. If I restart Zoneminder then the video sources go black (though still with current timestamps). I have to reboot the whole machine to get things back to normal again.

My guess is this is a problem with the card, but zoneminder seems to be happily buffering data to introduce a very big delay. Does anyone know what is really going on here and whether there is anything I can do short of replacing the card? I'd rather not do that -- it was difficult to source!

Zoneminder v1.25.0
Debian Linux 7
Linux 3.13-0.bpo.1-amd64 on x86_64
8 GB memory

[PacoLM]

Temperature affecting the framegrabber card?

[anagram]

Yes, that could be the cause. I do though have heatsinks on all eight video chips and it's in my garage, which is pretty cool. The CPU is running at 30 celsius right now.